1. Field of the Invention
The present invention is generally related to shipping pallets, and particularly to a load bearing structure for use on the deck of shipping pallets.
2. Description of Related Art
Shipping pallets are used as portable platforms to handle, store and transport, loads consisting of food, beverage, and most every product or product component produced. A pallet is typically made of wood and consists of slats and posts arranged to provide a top surface and open access underneath for a forklift-type device. Bottom slats may also be added to provide for transport on conveyer belts, for use in automated machinery, and to add strength, stiffness and rigidity to the pallet. The world market exceeds 1.5 billion pallets sold annually with the United States alone accounting for half a billion sales.
Present shipping pallets are usually constructed of wood or wood products with numerous associated problems. There are few shipping pallets constructed from alternative materials, but no matter what construction material is used, all present shipping pallets suffer from one or more significant problems, some of which are described herein.
Construction material choice has unintended consequences that significantly impact the end user and the world at large. Wooden pallets are heavy and often present rough and/or broken areas leading to work related injuries such as muscle strains, hernias, splinters or worse, and damage to the product being transported.
From the obvious issues surrounding logging, there are ecological issues now being addressed on a global scale. Wooden pallets play host to a wide variety of entomological pests and, as a consequence, introduce non-native species of destructive pests into foreign ecology systems. This problem has recently been recognized, and numerous countries around the world are enacting regulations to address it. Even more regulatory action is proposed, and international treaties, along with trade barriers against untreated wooden pallets, are already in force. The cost of wooden shipping pallets can only increase dramatically as preventative and safety measures now mandated are enforced.
One preventative action taken is the application of pesticides. Another preventative action is baking the wood material. However, the presence of pesticides introduces the risk of contaminating the product being carried on the shipping pallet and baking the wood increases the cost of the shipping pallet and still doesn""t address the issue of subsequent entomological infestation. Baking also increases fire danger because it dries out the wood, and increases the danger of splinters and the inevitable injury to workers using the pallet.
Disposal of wooden shipping pallets is an equally compelling problem. In the United States alone there are some 270 million wooden shipping pallets sent to landfills or burned yearly. Burning wooden pallets contributes to atmospheric pollution. With current and proposed entomological safeguards mandating pesticide treatment, the problem of pallet disposal becomes even more critical. The added factor of pesticide residue leaching into ground water or being released into the atmosphere through combustion exacerbates the problem. There have even been instances of pesticide-treated wood pallets contaminating the product they carry.
It would be a significant advantage to the art of shipping pallets to improve strength, weight, stiffness and rigidity, cost, design, versatility, production, transport, storage, reuse and recyclability, and ecological acceptability. Prior art amply demonstrates the attention inventors have paid to at least a few of these issues. U.S. Pat. Nos. 5,170,722; 5,365,859; 5,402,735; 5,417,167; 5,456,189; 5,497,709; 5,601,035; and 5,941,179 disclose various designs for prior art pallets.
U.S. Pat. No. 5,417,167 describes a modular plastic pallet design but falls short of the present invention in that the xe2x80x9cdeck boardsxe2x80x9d attachment method optionally requires added fasteners and reacts badly to the imposition of a unit load by loosening their grip or attachment to the xe2x80x9cstringers.xe2x80x9d It also describes a design that is decidedly weaker than the present invention and displays a lack of planar stiffness and rigidity that is overcome by the present invention.
U.S. Pat. No. 5,941,179 describes a modular plastic pallet design comprising two basic components that may be assembled into a variety of different pallet configurations to meet specific user needs. The runner to slat attachment means is weak, and the stiffness and rigidity of the design is less than that of the present invention. As with U.S. Pat. No. 5,417,167, this design is amenable to manufacture from a variety of raw materials, including thermoplastics, to eliminate the problem of wood pest hosting.
The present invention adds a number of novel and unique features to the shipping pallet art. For example, utilizing the present invention, shipping pallets can be manufactured mostly from recyclable materials. They can be manufactured from materials that do not support entomological infestation and that can be fire retarding. Structural load bearing characteristics of shipping pallets are enhanced through the utilization of an internal or exoskeleton of a high strength, lightweight material. Durability and impact resistance of the entire pallet structure is enhanced with the use of a suitable inner and/or outer form of a more ductile material. The shipping pallet is built as a compound structure so as to take advantage of varying shapes, sizes, materials and component arrangements to enhance strength, stiffness and rigidity, weight, entomological infestation resistance, fire resistance, and other physical characteristics. The composite design is suitable for any size or configuration of shipping pallet. It is stronger, lighter and more rigid than present shipping pallets. It is reusable for many service cycles, and then it is recyclable at the end of its useful life.
The structure disclosed herein features a combination of design elements that utilize the most effective geometric shapes to increase strength and reduce weight. It allows manufacture from a multitude of potential materials and even allows combinations of different materials within the same component so as to enhance desirable features. With the above stated improvements, the pallet disclosed herein satisfies a need in the marketplace and advances world commerce and preservation of the ecology.
In one embodiment, a load bearing structure includes arch elements placed adjacent to each other wherein tensile stresses, induced by a bending moment imposed upon on the structure from an applied load, are canceled or partially canceled by virtue of the arch elements"" direct or indirect interference with adjacent elements, which places the material of construction into compressive stress and creates an offsetting or partially offsetting compressive force within and between the elements.
In another embodiment, a load bearing structure is comprised of a plurality of arch elements rotated through some finite angle arranged so as to directly or indirectly contact adjacent like elements of some finite angle in order to place the material of construction into compressive stress canceling or partially canceling tensile stresses induced by a bending moment imposed upon the structure by an applied load.
In some embodiments, a plurality of the structural elements are extended longitudinally or laterally, or both, to create a large weight bearing surface area. In some embodiments, the arch elements are rotated through a lesser angle than 360xc2x0.
In one embodiment, the arch elements are oriented perpendicular to the imposed load. In another embodiment, the arch elements are oriented parallel to the imposed load. In yet another embodiment, the arch elements are oriented other than parallel or perpendicular to the imposed load. In yet another embodiment, the arch elements are oriented randomly in relation to the imposed load.